(Solved, I found a way)
Sorry about the lame title.
The second floor of my house has been lowered down to 6 clicks tall, using CFE. Then, I put 2 pieces of roof on top. I never remember the roof type names, but it is the very first roof in the game.
There is liveable room in the roof (attic), but how do my sims get there? I am missing something for sure.
If I use a spiral staircase on the ground floor, the landing is obviously on the second floor. But the second floor is only 6 clicks tall...so if I put a second spiral staircase on top, I land too high for the 3rd floor attic.
How am I supposed to do this?
Should the liveable room still be on the second floor?

I think, I'll try split level modular stairs instead..huh? I'll try that...
Ok, it seems to work with modular stairs but it is far from being pretty...

Ah! Here what works for this house anyway, a spiral stair + split modular. Now it's pretty.

Well, I ended up keeping the idea of a spiral staircase at the ground floor.
Then on the small second floor, I put a stage foundation. A modular stair goes down from it.
(Though, I also ended up remaking the lowered walls, this time to include casing for the stairs prior to lower it down.)
And finally, on the attic floor, another modular stairs going down to the stage foundation.
That is no mystery for CFE builder pros, but I never did this.

Will this helps?
I went in game to take screenies before you asked for them...
The pink house has a full/normal 3rd floor, but just in the back..where you see the smaller section of roof.
The front 3rd floor does not exist. The roof sits right on the lowered second/middle floor.

The house without siding has another type of roof..as there was no way of recreating the pink one with regular walls..hence why lowered wall are useful

OMG, the horror. LOL, just kidding, I see what you're trying to accomplish here and it looks pretty good.
As you might have expected, I will now try to accomplish the same thing without that pesky false level in-between. Pics later...

Well, it looks like your methods seems to be the best way after all, especially if you really want a steeper roof angle on one side of the house and a shallower one on the other. Plus dormers. Plus no CFE distortions so the wall covering stays looking nice.

I tried for about a half-hour an hour, since my previous post. Two storeys, with three shed roof sections, no dormers and distorted walls from the CFE - you probably wouldn't have liked it.
Sometimes the game is frustrating - sorry.

Roofs alone are frustrating...building can be a challenge.
I used this roof as I was trying to mimic an image I saw. But I will definitely use that lowering wall technique when I'll use other types of roofs as well. Not alllll the time of course.

Roofs alone are frustrating...building can be a challenge.
I used this roof as I was trying to mimic an image I saw. But I will definitely use that lowering wall technique when I'll use other types of roofs as well. Not alllll the time of course.

Yeah, I figured you were trying to mimic a real house, which can also be very hard to do - and frustrating.